E. Degl'Innocenti

Arabidopsis thaliana MYB75/PAP1 transcription factor induces anthocyanin production in transgenic tomato plants

Tomato (Solanum lycopersicum L.) cv. Micro-Tom plants were transformed with the Arabidopsis thaliana (L.)Heyhn. MYB75/PAP1 (PRODUCTION OF ANTHOCYANIN PIGMENT 1) gene. This gene encodes for a well known transcription factor, which is involved in anthocyanin production and is modulated by light and sucrose. Transgenic tomato plants expressing AtMYB75 were characterised by a significantly higher anthocyanin production in leaves, stems, roots and flowers under normal growth conditions. Further, they also exhibited anthocyanins in fruits. Anthocyanin accumulation was not widespread but took place in specific groups of cells located in epidermal or cortical regions or in proximity of vascular bundles. In all the organs of the transgenic plants, where AtMYB75 overexpression was determined, a clear increase in the accumulation of DFR (DIHYDROFLAVONOL 4-REDUCTASE) transcript was also detected. The expression of the tomato MYB-gene ANT1 (ANTHOCYANIN1), which had previously been identified as a transcriptional endogenous regulator of anthocyanin biosynthesis, was not altered. The higher basal content of anthocyanins in the leaves of the transgenic plants could be further increased in the presence of high light conditions and contributed to mitigate photobleaching damages under high irradiance.

The effect of salinity on photosynthetic activity in potassium-deficient barley species

The interactive effects of salinity and potassium deficiency on the growth, mineral elements and photosynthetic performance were investigated in wild (Hordeum maritimum L.) and cultivated barley (Hordeum vulgare L. var. Manel). At 28 d of growth, plants were treated with 3 mM K and 0 mM NaCl (3-0); 3 mM K and 100 mM NaCl (3-100); 0 mM K and 0 mM NaCl (0-0), 0 mM K and 100 mM NaCl (0-100) for 14 d. In both species, biomass production decreased considerably when the two constraints were applied simultaneously. Salinity affected shoots more than roots, whereas for potassium deficiency, the reverse occurred. Generally, potassium uptake was more affected in wild than in cultivated barley and, independent of potassium availability, 100 mM NaCl increased Na+ content in both species, whereas K+ deprivation increased Na(+) content only in H. maritimum shoots (0-0). Potassium-use efficiency (KUE) increased in all treated plants. Potassium deficiency increased the negative effects induced by salt in the photosynthetic process of H. vulgare, and this species seemed to be unable to counteract the negative effects of salinity. H. maritimum showed limitation in CO2 photoassimilation, but this species displayed mechanisms that play a role in avoiding PSII photodamage aimed to dissipate the excess energy.

Role of ascorbic acid in the inhibition of polyphenol oxidase and the prevention of browning in different browning-sensitive Lactuca sativa var. capitata (L.) and Eruca sativa (Mill.) stored as fresh-cut produce.

BACKGROUND Polyphenol oxidase (PPO) and, to a minor extent, peroxidase (POD) represent the key enzymes involved in enzymatic browning, a negative process induced by cutting fresh-cut produce such as lettuce (Lactuca sativa) and rocket salad (Eruca sativa). Although ascorbic acid is frequently utilised as an anti-browning agent, its mechanism in the prevention of the browning phenomenon is not clearly understood. RESULTS The activity of PPO and POD and their isoforms in lettuce (a high-browning and low-ascorbic acid species) and rocket salad (a low-browning and high-ascorbic species) was characterised. The kinetic parameters of PPO and in vitro ascorbic acid-PPO inhibition were also investigated. In rocket salad, PPO activity was much lower than that in lettuce and cutting induced an increase in PPO activity only in lettuce. Exogenous ascorbic acid (5 mmol L(-1)) reduced PPO activity by about 90% in lettuce. POD did not appear to be closely related to browning in lettuce. CONCLUSION PPO is the main enzyme involved in the browning phenomenon; POD appears to play a minor role. The concentration of endogenous ascorbic acid in rocket salad was related to its low-browning sensitivity after cutting. In lettuce, the addition of ascorbic acid directly inhibited PPO activity. The results suggest that the high ascorbic acid content found in rocket salad plays an effective role in reducing PPO activity.

Ozone tolerance in Phaseolus vulgaris depends on more than one mechanism.

Two bean cultivars with different sensitivity to ozone, i.e. the O3-sensitive Cannellino and the O3-tolerant Top Crop, were exposed to acute O3-stress (165 nL L(-1)) with the aim of evaluating physiological and biochemical traits that may confer O3-tolerance. Stomatal conductance was smaller and the ability to dissipate excess energy, via regulated and unregulated nonphotochemical quenching mechanisms was greater in Top Crop than in Cannellino. These morphological and physiological-traits allowed the O3-tolerant cultivar to compensate for the light-induced declines in PhiPSII, to preserve photosystem II from excitation-energy, and likely to prevent the generation of ROS to a superior degree than the O3-sensitive cultivar. Furthermore, the potential capacities to reducing the superoxide anion and H2O2 were significantly greater in Top Crop than in Cannellino. These findings are consistent with the early accumulation of H2O2, the almost complete disruption of cell structure, and irreversible damages to the photosynthetic apparatus observed in the O3-sensitive cultivar.

Effect of chronic O3 fumigation on the activity of some Calvin cycle enzymes in two poplar clones

The effects of long-term exposure to ozone (O3, 60 mm3 m-3 for 5 h d-1) on some Calvin cycle enzymes, in particular those modulated by the thioredoxin system, were studied in two poplar clones. These clones differ in sensitivity to O3. In the I-214 clone, the first effects from O3 treatment were seen after 40 d of fumigation, while the Eridano clone showed visible symptoms of damage after only 15 d of the treatment. Specific activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39) diminished in both the clones, while specific activity of phosphoenolpyruvate carboxylase (E.C. 4.1.1.31) increased. Exposure to O3 also caused a reduction in the specific activity of ribulose-1,5-bisphosphate kinase (E.C. 2.7.1.19) in both clones. At the end of the exposure to O3, specific activity of glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.13) increased in I-214 and remained similar to the control in Eridano, whereas specific activity of fructose-1,6-bisphosphate phosphatase (E.C. 3.1.3.11) was higher in Eridano and similar to the control in I-214.

mesophyll cell defective1 , a mutation that disrupts leaf mesophyll differentiation in sunflower

Mutants with altered leaf morphology are useful as markers for the study of genetic systems and for probing the leaf differentiation process. One such mutant with deficient greening and altered development of the leaf mesophyll appeared in an inbred line of sunflower (Helianthus annuus L.). The objectives of the present study were to determine the inheritance of the mutant leaf trait and its morphological characterisation. The mutation, named mesophyll cell defective1 (mcd1), has pleiotropic effects and it is inherited as a monogenic recessive. The structure and tissue organization of mcd1 leaves are disrupted. In mcd1 leaves, the mesophyll has prominent intercellular spaces, and palisade and spongy tissues are not properly shaped. The mutant palisade cells also appear to be more vacuolated and with a reduced number of chloroplasts than the wild type leaves of equivalent developmental stage. The lamina thickness of mcd1 leaves is greatly variable and in some areas no mesophyll cells are present between the adaxial and abaxial epidermis. The leaf area of the mcd1 mutant is extremely reduced as well as the stem height. A deficient accumulation of photosynthetic pigments characterizes both cotyledons and leaves of the mutant. In mcd1 leaves, chlorophyll (Chl) fluorescence imaging evidences a spatial heterogeneity of leaf photosynthetic performance. Little black points, which correspond to photosystem II (PSII) maximum efficiency (Fv/Fm) values close to zero, characterize the mcd1 leaves. Similarly, the lightadapted quantum efficiency (ΦPSII) values show a homogeneous distribution over wild type leaf lamina, while the damaged areas in mcd1 leaves, represented by yellow zones, are prominent. In conclusion, the loss of function of the MCD1 gene in Helianthus annuus is correlated with a variegated leaf phenotype characterized by a localized destruction of mesophyll morphogenesis and defeat of PSII activity.

Effects of Green Compost on Soil Biochemical Characteristics and Nutritive Quality of Leafy Vegetables

Green compost can improve the quality of fruits and vegetables through an increase in sugars and organic acids, which is extremely important because todays consumer is concerned about healthy and nutritional properties of food. The aim of this research was to evaluate the effects of green compost used as soil amendment on phenols and vitamin C content and on antioxidant capacity of leafy vegetables. Plants of Lactuca sativa var. acephala cultivar Red Salad Bowl and Spinacia oleracea cultivar Lorelay were grown in three soil treatments: a) 100% soil, b) 75% soil plus 25% compost c) 50% soil plus 50% compost. Results show that adding green compost to soil improved its fertility and the growth of plants. The use of compost for lettuce did not show any differences in antioxidant capacity and vitamin C content at either compost concentration (25 and 50%) while a significant reduction in phenols was evident. The Chl content decreased in spinach as a consequence of compost addition while no changes were observed in lettuce. However, the healthy properties of spinach decreased as a function of the compost concentration in the soil.

Role of ascorbic acid in the inhibition of polyphenol oxidase and the prevention of browning in different browning-sensitiveLactuca sativavar.capitata(L.) andEruca sativa(Mill.) stored as fresh-cut produce: AsA in PPO inhibition and browning prevention

BACKGROUND Polyphenol oxidase (PPO) and, to a minor extent, peroxidase (POD) represent the key enzymes involved in enzymatic browning, a negative process induced by cutting fresh-cut produce such as lettuce (Lactuca sativa) and rocket salad (Eruca sativa). Although ascorbic acid is frequently utilised as an anti-browning agent, its mechanism in the prevention of the browning phenomenon is not clearly understood. RESULTS The activity of PPO and POD and their isoforms in lettuce (a high-browning and low-ascorbic acid species) and rocket salad (a low-browning and high-ascorbic species) was characterised. The kinetic parameters of PPO and in vitro ascorbic acid-PPO inhibition were also investigated. In rocket salad, PPO activity was much lower than that in lettuce and cutting induced an increase in PPO activity only in lettuce. Exogenous ascorbic acid (5 mmol L(-1)) reduced PPO activity by about 90% in lettuce. POD did not appear to be closely related to browning in lettuce. CONCLUSION PPO is the main enzyme involved in the browning phenomenon; POD appears to play a minor role. The concentration of endogenous ascorbic acid in rocket salad was related to its low-browning sensitivity after cutting. In lettuce, the addition of ascorbic acid directly inhibited PPO activity. The results suggest that the high ascorbic acid content found in rocket salad plays an effective role in reducing PPO activity.